A great many intersections in the United States of America and Canada utilize the Opticom Priority Control System, a type of control system that provides intersection right-of-way to authorized vehicles. The system may be related to the technology found in the following U.S. Patents, which are incorporated by reference in their entireties into this application: 1) the Hamer U.S. Pat. No. 5,172,113 issued Dec. 15, 1992 and entitled System And Method For Transmitting Data In An Optical Traffic Preemption System; 2) the Hamer U.S. Pat. No. 5,187,476 issued Feb. 16, 1993 and entitled Optical Traffic Preemption Detector Circuitry; 3) the Hamer U.S. Pat. No. 5,187,476 issued Feb. 16, 1993 and entitled Optical Traffic Preemption Detector Circuitry; 4) the Hamer et al. U.S. Pat. No. 5,202,683 issued Apr. 13, 1993 and entitled Optical Traffic Preemption Detector; and 5) the Haagenstad et al. U.S. Pat. No. 5,602,739 issued Feb. 11, 1997 and entitled Vehicle Tracking System Incorporating Traffic Signal Preemption. This technology, or particularly the type of signals that are emitted by right-of-way vehicles, where these signals include a set of 14 pulses of light per second, can be put to great advantageous use a) because this technology is already part of a traffic system widely employed, b) because this technology, or set of 14 pulses of light per second, is being emitted freely without cost to a driver of a vehicle, c) because no additional structure or features are added to the traffic infrastructure, such as to traffic lights at intersection, and thus there is no added expense to the traffic infrastructure, and d) because there are no additional expenditures that would be required by the departments of transportation of the many states.
The Henry et al. U.S. Pat. No. 6,094,148 issued Jul. 25, 2000 and entitled Vehicular Emergency Vehicle Alarm Apparatus provides a demodulator connected between the sensor and the alarm for demodulating signals produced by the sensor and for generating an alarm signal only when the incident light is modulated at a frequency to which the demodulator is responsive. The demodulator includes a pulse counter coupled to the sensor for counting pulses produced by the sensor in a fixed length time period and an AND gate receiving the outputs of the pulse counter and the sensor for comparing pulses counted in the fixed length time period to at least one frequency to which the demodulator is responsive and for rejecting frequencies not corresponding to the modulated frequency to which the demodulator is responsive. The Henry et al. U.S. Pat. No. 6,094,148 details the detection of signals with the correct pulse repetition rate (frequency) and an unspecified sequential number of correctly spaced pulses (with what the Henry et al. patent terms a demodulator), using a discrete hardware pulse counter and AND gate. Hardware is electronic circuitry fixed at the time of design and built using physical components. This design once built may not be changed and is fixed at the time of construction. For example, a radio is designed and built as one, and forever will be one; and cannot be turned into a television. Function is fixed by the use of discrete hardware.